Update BUSL LICENSE to include licensed product and version. (#22357)

License /shamir under MPL.

Co-authored-by: hashicorp-copywrite[bot] <110428419+hashicorp-copywrite[bot]@users.noreply.github.com>

.copywrite.hcl

@@ -12,7 +12,10 @@ project {
     "ui/node_modules/**",
     "enos/modules/k8s_deploy_vault/raft-config.hcl",
     "plugins/database/postgresql/scram/**",
+    # licensed under MPL - ignoring for now until the copywrite tool can support
+    # multiple licenses per repo.
     "sdk/**",
     "api/**",
+    "shamir/**'"
   ]
 }